1. Field of the Invention
The invention relates to a turbomachine casing with containment structure intended to contain fractured rotating parts.
2. Summary of the Prior Art
The fracture of blades or the bursting of rotor discs carrying the blades gives rise to the risk of serious damage to important members of an aircraft incorporating the turbo-machines. In order to reduce the consequential damage, there have hitherto been employed, around the casing, structures capable of absorbing the energy of the fragments and of containing them within the engine enclosure.
An early prior proposal consisted in reinforcing the casing either by thickening of the metal in the annular zone surrounding the rotary blades, or by replacing a portion of the casing by an annulus of a metal of high mechanical strength. Thus the ejection of the fragments was avoided, but the latter, held within the casing were liable to cause further fractures and damage in the manner of a chain reaction. Furthermore, the mass of turbo machines thus equipped was substantially increased.
Another prior proposal described in French Patent Specification No. 2 375 443 consists in surrounding the blade stage with a retaining annulus of a material with high mechanical strength and of high specific weight. The annulus is supported through the intermediary of pins within an annular member secured to the structure of the turbo machine. As a result of impact the pins are sheared and the energy of rotation of the projected fragment is absorbed by rotation of the ring. This structure has enabled reduction in the risks of successive fractures in the manner of a chain reaction by the spacing the annulus and resultant improved arrest efficiency. However, as in the preceding example, this construction is heavy and bulky and this latter disadvantage renders it difficult for use in parts of a turbo machine where the bulk should be as low as possible.
Efforts of engine manufacturers have been directed up to the present time to lightening of the structure and the simplification of the mechanical construction. French Patent Specification No. 2 470 269 discloses a retaining structure comprising, considered in the radially outwards direction, a fluidtight detachable annulus constituted by a support covered by a wear layer, a structure of the sandwich type comprising a honeycomb between two skins, the internal skin being metal and the external skin of a synthetic resin reinforced by glass fibre fabric, and finally by an external layer of reinforcement of a composite fibrous material constituted by a windng of fibres embedded within a synthetic resin.
This arrangement enables substantial lightening of structure whilst maintaining a capability of maximum retention of debris having a high tangential velocity. However, it is neither possible to produce a continuous winding of fibres in the sector occupied by the auxiliary equipment mounting, nor even to arrange layers of material of honeycomb form between the casing and the mounting.
One object of the invention is the production of a retaining structure of complex form capable of being used even in sectors where the presence of auxiliary equipment does not allow the incorporation of thick containing structures. This applies particularly to the zone surrounding the blades of the fan of a twin flow jet engine and even more particularly to the sector in which the equipment mounting lies, the latter particularly requiring protection against possible impact of a fragment derived from the fan.